Heat exchange apparatus and method of operating the same



G. C. DERRY Oct. 6, 1931.

HEAT EXCHANGE APPARATUS AND METHOD OF OPERATING THE SAME Filed July 21,1928 2 Sheets-Sheet l 1g.Z 2a 16' W24 Wness Jhvenior Oct. 6, 1931. I G.c. DERRY 1,825,656

HEAT EXCHANGE APPARATUS AND METHOD OF OPERATING THE SAME Filed July 21,1928 2 Sheets-Sheet 2 0000000 L JZ 1 .56 i 56 J l E Witness WAaQMMPatented Oct. 6, 1931 UNITED STATES PATENT OFFICE GARDNER G. DERBY, OFSHARON, MASSACHUSETTS, ASSIGNOR TO B. F. STURTEVANT COMPANY, OF HYDEPARK, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS HEATEXCHANGEAPPARATUS AND METHOD OF OPERATING THE SAME Application filedJuly 21,

The present invention relates to heat exchange apparatus and to methodsof operating such apparatus, and more particularly to that type ofapparatus and method of operating which are especially adapted for usewhere it is desired to effect a transfer of heat between a gas and aliquid as, for example, an economizer for heating boiler feed water.

The objects of the present invention are to provide a heat exchangeapparatus of the above type and a method of operating the same whereby acompact and inexpensive construction may be secured, capable of beingquickly and easily installed and repaired, of

high capacity and efliciency in operation, and

suitable for use under widely varying conditions of gas and fluid flow.

With these objects in view, the present invention comprises a heatexchange apparatus in which provision is made for the properdistribution of flow of the liquid in its passage through the apparatus.This includes a plurality of series-connected sections. each sectionconsisting of a pair of headers and a plurality of tubes through whichthe liquid flows in parallel. A feature of the invention COI1SlStSxlIlfi construc tion whereby the liquid is distributed ub:

80 stantially equally-among all of the tubes'in each section. This iscarried out in thefprer ferred form of the invention by arranging thjinlet and outlet of a section at diagon ly oppos te corners thereof, inorder that the length of the path of flow from inlet to outlet throughany tube will be equal to the path through any other tube. Theresistances to flow by all paths in a section will therefore besubstantially equal, and a substantially equal division and flow of theliquid is assured. 1

here the apparatus is of such size that the resistance ofseries-connected sections would be large, the invention contemplatesdividing the sections into a plurality of branches or paths having acommon supply and discharge whereby the liquid flows through theseparate branches or paths in parallel.

In order to secure mosteflicient operation 1928. Serial No. 294,484.

of the economizer, not only must the rate of flow through the severalbranches or paths be substantially the same, but each branch must besubjected to the same heating effect. The former is secured bymaking'the paths or branches alike or symmetrical with respect to eachother so that the same capacities are obtained and the same resistancesdeveloped. The latter condition is fulfilled by arranging the paths orbranches so that each traverses substantially the same portions of theheated gases as all the others.

Another feature of the present invention is the prevention of internalconvectional circulation and this advantage is secured by increasing thevelocity at certain points in each branch or path yet without increasingthe velocity through the main portions of the branches or unduly raisingtheir resistance. Such increased velocity at these points effectivelyprevents any reversal of flow under the relatively weak convectionalforces. This is a feature of advantage since'it ada' ts the economizerfor use with down flow 0 water and up flow of gas as well as up flow ofwater and down flow of gas.

Other features of the invention consist in certain novel features ofconstruction, combinations and arrangements of parts, hereinafterdescribed and particularly defined in the claims.

In the accompanying drawings illustrat ing whatis now considered thepreferred form of the invention as embodied in an economizer for heatingboiler feed water, Fig. 1 is a side elevation of a unit of theeconomizer with a portion of the'casing broken away; Fig. 2 is ahorizontal sectional view of a single section of the economizer taken onthe line 22 of Fig. 1; Fig. 3 is a diagrammatic sectional end elevationshowing the arrangement of the sections in the casing; Fig. 4 is adetail view in side elevation showing a modified arrangement of thesections and Fig. 5 is an end elevation ofthe apparatus shown in Fig. 4.

The illustrated embodiment of the invention comprises an economizerhaving a plurality of horizontal sections through which water passes tothe boiler and over which the hot gases from the boiler flow to heat thescribed in detail.

water. The economizer casing is arranged over the boiler, the gasespassing upwardly through the economizer, and the water [lowmg downwardlythrough the econonnzer 111 counter-current to the gases.

Referring to Fig. 3, the casing or fluelG for the gases includes aplurality of econom izer sections 8, each section consisting of a frontand a rear horizontal.header and a plurality of horizontal tubes, aswill later be de- The sections 8, of which there are twenty in theillustrated embodiment of the invention, are arranged in five.

bypass flue being controlled by dampers 16.

The water is admitted to the top section and flows downwardly throughthe twenty sections to be discharged at the bottom into the boiler.

Referring to Figs; land 2, each section comprises a plurality ofhorizontal tubes 18, preferably of steel to withstand the high pressuresemployed in modern practice. and connected at their ends into thehorizontal headcrs 20 and 22. As shown in Fig. 2, each section comprisesnine tubes. Each tube is provided on its outer surface throughout itslength with spaced disks or fins 24 to. increase the heat transfercapacity of the apparatus.

' The disks are preferably secured upon the tube by passing an expandingtool through the tube while the disks are maintained spaced is thencoated inside and out with a lead coat-- ing to IQSlSll both lnternaland external corroslon.

The sections are supported in the casing by angle irons 26 which aresecured to the sides of the casing and onwhich' the-endsof the headersrest. An intermediate support for the middle of each section comprises aproper and not'with the flue; The ends of the channel rest upon theangle irons 26. A single section may be conveniently inserted orremovedby' slidingit along its pair of angle iron supports.

As shown in Fig. 2, the tubes'arc notsymmetrically arranged with respectto the ends of the headers. The d stance between the ends of the headersand the tube 18 at one side of the section is greater than the distancefrom the ends of the headers to the in Fig. 2; The distance B in thepreferred form of the invention is approximately equal to the centerline distance between tubes in the same horizontal row, and the distanceA is greater than B by one-half the center line separation betweentubes. It will therefore be seen that if alternate sections areinverted, that is,- turned either end for end or upside down about thelongitudinal axis, (but not both ways,) with the ends of their headersin alignment, the tubes will be staggered vcr-. ti'cally, as shown inFig. 3.

In order that the connections between headers may be Verticallyarranged, the inlet and outlet openings of the headers must be locatedat equal distances from the ends of the headers. Thus the header 20hasan inlet opening 31 and the header 22 hasan out-let opening 32, thecenters of both of these openings being arranged at the'same distance Afrom the end of the header. The opening 31 will therefore be disposeddirectly opposite the tube 18 but the opening 32 in the opposite headerwill have its center intermediate to the tube 18 and the tube adjacentthereto.

The openings. 31 and 32 which provide for connections between sectionsare disposed at diagonally opposite corners of the section, the openin31 being at one end of the header 20 and the opening 32 being at theopposite endof the header 22. This diagonal arrangement'of the inlet andoutlet insures that all the water passing through the section willtraverse the same length of path. that is to say, assuming the opening31 to be an .inlet and the opening 32 an outlet. the total length of anypath of the water from inlet to outlet will be equal to the length ofone tube plus the length of one header. The lengths of all possiblepaths of flow through one section being equal, the resistances of theparallel flow will be substantially equal.

and an equal division of water through all the tubes of the section isassured.

In order to afford means for securing the ends of the tubes in theheaders. each header is provided opposite the tube openings with toolinserting openings which are subse quently closed by plugs 34. The toolemployed is preferably a rotary expander having a flexible shaft topermit the tubes near the inlet and outlet openingsfil and 32 to beoperated upon.

Water'is admitted to the top section through an inlet pipe 36 andconnections between sections are afforded by return bends 38.. As shownin Fig. 1, the top section has a front header. 20 to which the inletconnection 36 is boltedand a rear header 22 to which the return bend 38is connected to permit flow of water to the next section below; Thisnext section comprises a rear header 20 and a front header 22'and issimilar to the first section except for being turned around, so that theinlet of the second section will be directly under the outlet of the topsections. The third and fourth sections are respectively identical tothe first and second sections. In each case, therefore, the type 20header comprises an inlet header and the type 22 forms the outlet headerfor any given section.

The top unit which consists of four sections is connected to the nextunit below by a long bend'40. The other sections and units in theeconomizer are similarly connected and a suitable connection is takenfrom the rear of the bottom section to conduct the feed water to theboiler.

In some instances where an economizer of considerable horizontal lengthor vertical height is necessary in order to effect the necessary heattransfer, the apparatus above de-' scribed will introduce a waterresistance too high to be economically overcome by the feed pump. Insuch event the present invention contemplates arranging the sections fora plurality of parallel paths of flow. This arrangement is shown inFigs. 4 and 5, wherein an economizer of the same number of sections isarranged so that the water divides and flows in two parallel branches orpaths.

Considering the upper group'or unit of four sections shown in Figs. 4and 5, the water is admitted from the supply connection which dividesthe water into two paths flowing to the Ts 52 and 54 and thence into thedown pipes 56 and 58, respectively. The T connection is employed toafford flanges 59 for mounting of safety valves. The pipe 56 comprisesan inlet pipe similar to the in let 36 of the single path constructionpreviously described. It enters a top section which has a front header20 and a rear heador 22. The section next below is connected with theinlet pipe 58 at the opposite side of the apparatus. This section alsocomprises a front header 20 and a rear header 22. both being turnedupside down, however, with respect to the top section in order that thetubes ma be staggered, as clearly shown in Fig. 5. he third section isexactly similar to the top section and is connected to the top section.sixth sections forming a part of the second group.

- fourth, etc. sections of the economizer. The

two paths oin at the front of the economizer in a common discharge 68 atthe bottom. For the same number of tubes and sections and therefore thesame heating surface, this econvi omizer has a total resistance onlyone-fourth that of the single path or series section economizer of Figs.1 and 2. These two paths, it will be noted, are alike or symmetricalwith respect to each other, and have the same number of sections, tubes,and connections all similarly arranged, so that the capacities andresistances of the two paths are substantially identical, insuring thesame 'flow through each. Furthermore, each path traverses the sameportions of the fine or gas stream so that each is subjected to the sameheating effect;

Thus the first and third sections of each group which form part of thepath entering through branch 52 and connection 56 extend entirely acrossthe gas stream. In a similar manner, sections 2 and 4 of each groupwhich are included in the second path of flow entering throughconnections54 and 58 extend envery slight, but as a matter of fact thetemperature of the gas impinging upon the tubes of adjacent sections issubstantially the'same. This is obvious when it is considered that noneof the sections is exposed to the radiant heat of the furnace but onlyto the hot waste gases, and these gases suffer a reduction intemperature only by contact with the econo. mizer tubes. Since the tubesare staggered,

the tubes of the higher of each pair of sections, beginning at thebottom, are swept by gas which'has passed between the tubes of thelowest section without loss of temperature. Thus, each pair of adjacentsections, although lying in differentpaths and at slightly differentheights in the economizer. rc-

ceive substantially the same amounts of heat. As a result, the maximumefficiency in operatron will be secured and liability of'internalconventional currents due to unequal temperatures in the two paths willbe avoided.

It will alsobe noted that the connection from one header'to another isby a single pipe or bend which. whileof greater diameterthan theindividual tubes, is very much smaller in cross-sectional area than thetotal crosssectional tube area of the sections, preferably less thanone-half. Since all of the water of a section must pass throu h a singleconnection, it follows that the velocity of flow through such connectionwill be correspondingly greater than through the tubes, preferably atleast twice as great. Such increased velocity will effectively preventany tendency in either path to reverse its direction and flow upwardlyunder convectional action which necessarily is relatively weak beingbased upon difference in weight of the water in the two paths, due todifference in temperature. Since the main portions of the paths arecomposed of the tubes in parallel with correspondingly low resistanceand velocity, but little additional work is thrown upon the pump.

It will be seen that the invention afi'ords provision for assuringpractically uniform distribution of water at all points where par,-'allel flows occur. Thus, in any section there is assured a substantiallyequal distribution of water among the tubes, and where the parallelbranch flow construction is employed, the water is also forced to dividein practically equal quantities through the separate branches and issubjected to substantially e ual heating in each branch. Operation of te economizer with either up or down flow of water and at high efficiencyand with maximum heat transfer at all times is consequently attained.

Although the economizer of Figs. 4 and 5 has been illustrated anddescribed as comprising two parallel flow branches, it may obviouslyconsist of a larger number of branches, if it is desired to decrease thetotal resistance to an even lower value. In such case, the separatebranches will each comprise the same number of sections disposed andarranged to subject the water in each branch to substantially the sameheating efiect.

In the illustrated embodiment of the present invention the tubes areprovided with fins on their outer surfaces in order to increase thesurface exposed to the gas and thereby facilitate the transfer of heatfrom the gas to the tube. While this is not an essential feature of theinvention, it is of advantage since it enables the same amount of heatto be transferred to a given volume of water in a much shorter period oftime, thus not only reducing the size of the economizer for a givenoutput and correspondingly reducing the internal resistance and hencethe work required of the pump, but increasin the velocity of flowthrough the tubes an connections. This increased velocity through theeconomizer as a whole, supplementing the localized increase in velocityin the connections or bends between the sections due to their relativelysmaller cross-sectional area, makes even more remote the possibility ofreversal of flow through such connections or bends and still furtherinsures the proper and efficient operation of the economizer with downflow of water.

The present invention has been shown and described as embodied in aneconomizer comprising a plurality of vertically disposed sections havinghorizontal tubes located in a vertical gas flue, but it will be apparentto those skilled in this art that many features of the present inventionare equally applicable to the familiar and common type of economizerwherein the series of sections and the flue are horizontally arranged.

Havin thus described the invention, what is claime is:

1. A heat exchange apparatus comprising a plurality of sections eachhaving a front header and a rear header and tubes connecting theheaders, the headers having diagonally opposed openings for inlet andoutlet whereby the paths through all tubes of the section are ofsubstantially equal length, and

a connection between the inlet opening of 3. A heat exchange apparatuscomprising a plurality of sections each having a front header and a rearheader and tubes connecting the headers, each header having an inlet andoutlet opening, and connections between the inlet and outlet openings ofa pair of sections, the connections being of materially lesscross-sectional area than the total crosssectional area of all the tubesof a section.

4. A heat exchange apparatus comprising a plurality of sections eachsection consisting of a front header and a rear header and a pluralityof tubes connecting the headers, the sections being arranged in aplurality of branches for parallel flow through the branches, and meansfor connecting all of the sections of the separate branches in series,and a common supply and discharge connections for all of the branches.

5. A heat exchange apparatus comprising a plurality of sections, eachsection consisting of a front header and a rear header and a pluralityof tubes connecting the headers, the sections being arranged in aplurality of branches for parallel flow through the branches, and meansfor connecting in series all of the sections of each separate branch,the connecting means for adjacent sections comprising a single pipe ofmaterially less cross-sectional area than the total cross-sectional areaof all of the tubes in one of said sections.

6. A heat exchange apparatus comprising a purality of parallel flowbranches having a common supply at the top and discharge at the bottom,each branch including a vertical series of horizontal sections havingheaders and connecting tubes, a single vertical pipe connection betweeneach of the adjacent seca plurality tions of the separate branchesconstructed and arranged to cause materially higher velocity of flowthrough said pipes than through the tubes, and means for passing hot gasupwardly over the sections.

7. A heat exchange apparatus comprising a plurality of parallel flowbranches having a common supply at the top and a common discharge at thebottom, each branch including a vertical series of horizontal sectionshaving headers and a plurality of connecting tubes provided with fins toafford increased heat absorbing surface, and a connection between eachpair of adjacent sections said connections being of less cross-sectionalarea than the total cross-sectional area of the tubes of one of thesections.

8. A heat exchange apparatus comprising of superposed horizontalsections each consisting of a pair of headers and a plurality ofparallel connecting tubes, the sections being arranged in a plurality ofbranches, the separate branches including regularly spaced andnon-contiguous sections, means for connecting the regularly spacedsections of the separate branches in series, and a common supply and acommon discharge for the branches.

9. A heat exchange apparatus comprising a plurality of superposedhorizontal sections each consisting of a pair of headers and a pluralityof parallel connecting tubes, the sections being arranged in twobranches, the separate branches including alternate sections, means forconnecting the sections of the separate branches in series, and a commonsupply at the top and a common discharge at the bottom for the branches.

10. A heat exchange apparatus comprising a plurality of horizontalsections each having an inlet header and an outlet header and a singlerow of tubes having extended heating surface and providing a pluralityof parallel paths of flow between the headers, the headers havingdiagonally opposed inlet and outlet openings to make the several pathsof flow through the different tubes substantially uniform, the sectionsbeing arranged in a plurality of branches, pipes connecting the sectionsof several branches in series, and supply and discharge connections atthe top and bottom of the apparatus for connecting the branches forparallel flow, the connecting pipes between sections being of reducedarea relative to the total tube area of a section.

11. A heat exchange apparatus comprising a flue for the hot gas and aseries of sections each extending across the flue, and comprising afront and a rear header and a single row of tubes between the headers,the headers having diagonally opposed inlet and outlet openings, and asingle pipe connection between the inlet and outlet openings of a pairof sections.

12. A heat exchange apparatus comprising a. flue for the hot gas and aseries of sections each extending across the flue, and comprising afront and a rear header and a single row of tubes between the headers,the sections being arranged in a plurality of branches, pipes forconnecting togetherthe sections of each branch in series, and a commonsupply and common discharge for the branches.

13. A heat exchange apparatus comprising a vertical flue for the hotgas, a series of superposed horizontal sections extending across theflue, each section comprising a pair of horizontal headers and a singlerow of parallel tubes therebetween having fins to provide increased heatabsorbing surface, the headers having diagonally opposed inlet andoutlet, the sections being arranged in a plurality of. branches, asingle pipe for connecting together adjacent pairs of sections of theseparate branches in series, the sections ofeach branch being separatedfrom one another by sections of another branch, and the tubes ofcontiguous sections being staggered, and a common supply and dischargefor the branches.

14. A heat exchange apparatus comprising a plurality of verticallysuperposed horizontal sections arranged in a plurality of branches, eachbranch including a plurality of sections the adjacent sections of eachbranch being separated by sections of another branch, means forconnecting the sections of the several branches in series, and means forconnecting the branches in parallel.

15. A section for heat exchange apparatus comprising two headers eachopen interiorly throughout its length, and having inner and outer walls,a single row of tubes extending between the inner Walls of the headersand provided with fins to increase the heat absorbing surface, theheaders having one an inlet and the other an outlet opening in the outerwalls at diagonally opposite corners of the section.

16. A section for heat exchange apparatus comprising two headers, aplurality of tubes connecting the headers, the tube at one side of thesection being spaced from the ends of the headers a distance greaterthan the spacing of the tube at the other side of the section by adistance equal to one-half the tube spacing, the headers having inletand outlet openings at substantially diagonally opposite corners of thesection.

17. A section for heat exchange apparatus comprising two headers, aplurality of tubes connecting the headers, the tube at one side of thesection being spaced from the ends of the headers a distance greaterthan the spacing of the tube at the other side of the section by adistance equal to one-half the tube spacing, the headers having inletand outlet site corners of the section, the openings being at equaldistances from the ends of the headers.

18. The method of operating a heat exchange apparatus which consists incausing the gas to pass upwardly in a stream and the liquid to passdownwardly in a plurality of separate streams and subjecting each liquidstream to substantially the same portions of the gas stream atsubstantially the same temperature whereby each liquid stream receivessubstantially the same heating effect.

19. The method of operating a heat exchange apparatus which consists incausing the gas to flow upwardly in a stream and the liquid to flowdownwardly in a plurality of streams, and passing the liquid of eachstream in a plurality of separate fpaths through the I gas stream, eachstream 0 liquid traversing substantially all portions of the gas streamwhereby each stream is subjected to substantially the same heatingeffect.

20. The method of operating a heat exchange apparatus which consists incausing the gas to flow upwardly in a stream and the L liquid to flowdownwardly in a plurality of streams, passing the liquid of each streamin a lurality of parallel paths across substantially the entire gasstream at a plurality of separated points along said gas stream,

i change apparatus in which the and passing the liquid of each streamfrom point to point along the gas stream in a single path,

21. The method 01 operating a heat exas flows upwardly in a stream andthe liquid flows downwardly in a plurality of separate streams whichconsists in passing each liquid stream horizontally across substantiallythe entire gas stream, and downwardly at a linear velocity, greater thanthe linear velocity oi the said liquid stream passing horizontally.

In testimony wg lereof T have signed my name to this speci cation.

GARDNER C. DERBY,

